The present invention is generally related to a method for suppressing the optical proximity effect (OPE) bias within a wafer, and more particularly to a method for compensating the optical proximity effect bias within a wafer such that the OPE result is fixed from die to die within the wafer.
With respect to the semiconductor fabrication processes, the lithography process occupies a decisive factor in the performance of the manufactured semiconductor device. The result of the lithography process may seriously affect the integration level of the manufactured semiconductor device. The lithography process is to utilize the exposure principle of optics to transfer the pattern from the photomask onto the surface of semiconductor wafer, and then an etch process is performed according to the transferred pattern so as to manufacture the desired semiconductor device.
Nonetheless, the occurrence of the well-known optical proximity effect (OPE) is an inevitable concern during semiconductor fabrication process. OPE is resulted from the absence of higher-order diffraction order during the image formation process, and it will negatively affect the accuracy and resolution of the transferred pattern. Consequently, OPE will result in a severe change of critical dimension and make the profile of the semiconductor structure formed thereby out of shape. Moreover, because the properties, such as thickness, type, reflectivity of the substrate film and/or the type, thickness of the selected photoresist material, are not uniform, it will cause the OPE result to be different from die to die within a wafer and thus the performance is different from chip to chip.
In convention, the exposure process is carried out in an exposure equipment, such as a stepper. The exposure process is carried out in a manner known as xe2x80x9cstep and repeatxe2x80x9d. The exposure parameters and exposure condition setup in every exposure step, however, is fixed. Please refer to FIG. 1 showing the reflectivity of the silicon nitride film across a wafer. It will be understood that the reflectivity is increased gradually from the center region of the wafer to the edge region of the wafer. If the properties, i.e. thickness, reflectivity etc., are not uniform, the OPE result will differ from die to die within the wafer and the quality of manufactured semiconductor device will be affected.
There arose a need to suppress the optical proximity effect bias within a wafer by compensating the optical proximity effect bias from die to die within the wafer.
It is therefore an object of the present invention to provide a method for suppressing the optical proximity effect bias within a wafer by compensating the optical proximity effect bias from die to die within the wafer.
It is further an object of the present invention to provide a method for producing chips with the same quality and performance control.
According to the present invention, the method for suppressing the optical proximity effect within a wafer includes the following steps: Firstly, performing a first exposure step with a first exposure parameter setup to transfer a pattern from a photomask to a first die of a wafer. Secondly, performing a second exposure step with a second exposure parameter to transfer the pattern from the photomask to a second die of the wafer, wherein the first and second exposure parameter setups are adjusted according to the local optical proximity effect bias of the dies within the wafer.
In accordance with the present invention, the wafer is further coated with a silicon nitride substrate film.
In accordance with the present invention, the exposure parameter setup is a numerical aperture setup.
In accordance with the present invention, the exposure parameter setup is a partial coherence setup.
In accordance with the present invention, the exposure parameter setup is an exposure energy setup.
In accordance with the present invention, the exposure parameter setup is an exposure time setup.
In accordance with the present invention, the exposure parameter setup is an exposure light intensity setup.
In accordance with the present invention, the exposure parameter setup is a focus setup, more preferably, a best focus setup.
In accordance with the present invention, the light source used in the exposure steps is an I-line.
In accordance with the present invention, the light source used in the exposure steps is a G-line.
In accordance with the present invention, the light source used in the exposure steps is an KrF laser.
In accordance with the present invention, the light source used in the exposure steps is an ArF laser.
In accordance with the present invention, the light source used in the exposure steps is a X-ray.
In accordance with the present invention, the light source used in the exposure steps is an e-beam.
In accordance with the present invention, the exposure steps are performed by an exposure equipment, such as a stepper or a scanner.
Now the present invention may best be understood through the following descriptions with reference to the accompanying drawings, in which: